1. Field of the Invention
The invention pertains to the use of contact holography to form multiple holograms and, more particularly, to the use of contact holography and a master hologram to make replica gratings, lenses, switches and other images wherein one or both of the master hologram and corresponding replica comprise a polymer-dispersed liquid crystal (PDLC) material.
2. Description of the Related Art
Once a hologram has been recorded, whether using simple or complex optical geometries, it is often desired to reproduce or reconstruct the hologram so as to have multiple copies which are substantially identical to the originally recorded hologram. There are numerous methods for reconstructing holograms, however these are cumbersome and involve retracing the steps used to create the original or master hologram. Unfortunately, where complex geometries are involved, this is neither an efficient nor a practical method for performing mass reconstruction.
By way of example, U.S. Pat. No. 3,580,655 to Leith (xe2x80x9cLeithxe2x80x9d) which is incorporated herein by reference, sets forth multiple methods both for formation of the master hologram and for reconstruction of the master hologram, either for viewing or for permanent recording. While the subject matter of the current invention is not centered on the formation of the master hologram, the advantages of the current invention are readily apparent when the complexity of this initial formation is recognized. For example, FIG. 1 (FIG. 7 of Leith) illustrates one of the simplest geometries for forming a master hologram. This simple configuration illustrates the basic components for simple holographic construction, including a coherent light source 10 emitting an incident beam 12. From this incident beam 12, two separate beams are formed. A prism 14 or similar light-splitting or directing device intercepts part of the incident beam 12 and directs a reference beam 16 to a detector plate 18. Simultaneously, a part of the incident beam is diffused by a diffusion screen 20 and diffracts off an object 22, forming an object beam 24, which also passes onto the detector plate 18. The interaction between the reference beam 16 and the object beam 24 produces an off-axis hologram, in the form of multiple Fresnel patterns and interference fringes.
Further in Leith, there is a method and system for using the master hologram from FIG. 1 to produce replicas of the master hologram. FIG. 2a represents the simplest system and method for duplicating the master hologram. Referring to prior art FIG. 2a, there is an incident beam 12 from a coherent light source 10 which forms two separate beams, a reference beam 16 and an object beam 24. In this case, object beam 24 results from the interaction of part of incident beam 12 with the master hologram 26. Due to the grating effect of the master hologram 26, the object beam is directed along the formation angle and a detector 18 is placed at the intersection of the reference beam 16 and the object beam 24, forming a replica of the interference pattern comprising master hologram 26. In this case, the object beam forms a virtual image of master hologram 26 which is recorded on the detector 18. The real image is not used in the reproduction process.
As is clear to one skilled in the art, this method of master hologram duplication, while viable, results in a number of disadvantages. In any situation involving light traveling through an optical train, there is the potential for misalignment of the optical elements. Further there are inherent efficiency limits for each optical element. These disadvantages can result in unwanted diffraction, reflection, and in some cases aberration of the beams. Additionally, while lasers have improved coherence parameters, coherence length remains an issue. Even the simplest dual beam recording and duplication systems described above require precise alignment for optimal results. The conventional systems above also require multiple optical elements even for the simplest holographic formation geometries. Consequently, complex geometry hologram formation is not available with the Leith system because of the length and requisite multiple components of the optical train.
The prior art also contemplates a single beam master hologram duplication system that greatly reduces the number of necessary optical components. Referred to as contact printing, this system for duplicating a master hologram resembles in many respects the art of photography. The master hologram and a holographic detection plate (e.g., emulsion plate) are placed in optical contact with one another and exposed to light. Photographic development of the holographic detection plate results in a replica master hologram. For a fully successful reproduction, the optical contact between the master hologram and the holographic detection plate must be such that there is no loss of resolution within the interference fringes. Establishing the requisite optical contact has proved to be a significant limiting factor in attempts to use contact printing for duplication of holograms. Consequently, the prior art single-beam contact printing method, though it reduces the number of optical elements necessary for duplication of a master hologram, poses new optical hurdles to the art of hologram replication.
Referring to FIG. 2b, a prior art single beam contact printing system is illustrated in accordance with U.S. Pat. No. 5,547,786 to Brandstetter, et al. (xe2x80x9cBrandstetterxe2x80x9d), the specification of which is incorporated herein by reference. The system of Brandstetter includes a source of monochromatic, collimated light of substantially fixed wavelength such as laser 10 which produces an output beam 12, referred to as the replication or recording beam, and directs that beam through beam conditioning means 80, which preferably comprises lenses 82 and 84, pinhole 86, and filter 88. Lenses 82 and 84 and pinhole 86 are provided to collimate beam 12 and to expand that beam to the desired size filter 88 is provided to control or adjust the intensity or amplitude of beam 12 across its profile as desired. Subsequent to conditioning by means 80, the conditioned beam 12 is directed at a desired angle onto master holographic optical element 26, passes through, and directly enters a phase recording medium 18, such as a photopolymer layer that has been applied onto the backside of the master holographic optical element.
The method for forming the replica within the photopolymer layer requires a polymerization step which is separate from the recording step. Further, the resulting replica hologram is not switchable. Further, the recording mediums currently available as blanks for hologram duplication are limited in their ability to provide optimal optical contact with the master hologram.
Accordingly, there remains a need for a system and method for mass reproduction of holograms, having a single beam contact printing method using an optically superior recording medium.
In conventional contact holography methods and systems, situations exist wherein the use of a static, as opposed to a switchable, master hologram is limiting. First, a static hologram is limited to a single diffraction efficiency, which is always ON (i.e., it cannot be turned OFF). Second, even though a non-recording wavelength theoretically should pass through the static hologram without causing recording in the blank, in practice this is not the case. Instead, a non-recording, incoherent wavelength passing through a static master may result in unwanted scattering and cross-coupling of phase information which can decrease diffraction efficiency, introduce cross-gratings, increase haze, and generally decrease the signal-to-noise properties of the replicated grating. These limitations of the static master hologram result in difficulties with contact recording schemes that require either in situ pre-recording or post-recording irradiation of the blank.
Accordingly, a need remains for a non-static master hologram for use in a contact printing method and system.
The present invention offers increased efficiency and quality in the duplication of a master hologram utilizing an improved method and system of contact printing. A first embodiment of an improved method and system of contact printing employs a polymer-dispersed liquid crystal (PDLC) recording medium as the duplication blank. The optical qualities of the PDLC material described herein provide an improved method of duplication using single beam contact printing regardless of the material comprising the master hologram. Thus, master holograms originally recorded using highly complex optical geometries (e.g., computer generated holograms) are capable of duplication without the need for multiple beam power/intensity balancing and long recording times. The improved hologram contact printing method and system described herein works with virtually any type of master hologram, including both reflection and transmission holograms.
A first embodiment of the present invention describes a system for duplicating a hologram which includes a radiation source for emitting a coherent beam of radiation, a hologram, and a recording substrate comprised of a polymer-dispersed liquid crystal material for recording a replica of the hologram therein. The components of the system are arranged such that the hologram and the recording substrate are in optical contact with one another and they are placed in a path of the coherent beam of radiation.
A second embodiment of the present invention describes a method for duplicating a hologram which includes the following steps of (1) directing a coherent incident radiation beam at a first optical component; (2) transmitting the coherent incident radiation beam through the first optical component forming a transmitted beam, to a second optical component having a hologram recorded therein; and (3) diffracting the transmitted beam via the hologram forming a diffracted radiation beam. The incident beam and the diffracted beam interfere within the first optical component to form a replica of the hologram therein.
A third embodiment of the present invention describes a method for contact recording at least one hologram which includes the following steps of: (1) directing a coherent radiation beam at a first optical component having a hologram recorded therein and (2) diffracting a first portion and transmitting a second portion of the coherent radiation beam through the first optical component to a second optical component. The transmitted beam and the diffracted beam interfere within the second optical component to form a replica of the hologram therein.
A fourth embodiment of the present invention describes a method for contact recording at least one hologram which includes the following steps of: (1) optically contacting at least one master hologram to at least one holographic blank to form a master/blank assembly; (2) exposing the master/blank assembly to a pre-recording beam; (3) exposing the master/blank assembly to a recording beam; and (4) exposing the master/blank assembly to a post-recording beam, wherein the master/blank assembly remains optically contacted throughout each exposure.
A fifth embodiment of the present invention describes a method for contact recording at least one hologram which includes the following steps: (1) optically contacting at least one master hologram to at least one holographic blank to form a master/blank assembly; (2) exposing the master/blank assembly to a recording beam; and (3) exposing the master/blank assembly to a post-recording beam, wherein the master/blank assembly remains optically contacted throughout each exposure.
A sixth embodiment of the present invention describes a system for contact recording at least one hologram which includes at least one master hologram, at least one holographic blank, a pre-recording beam, and a recording beam, wherein the at least one master hologram and the at least one holographic blank are in optical contact during exposure to the pre-recording beam and the recording beam.
A seventh embodiment of the present invention describes a system for contact recording at least one hologram which includes at least one master hologram, at least one holographic blank, a recording beam, and a post-recording beam, wherein the at least one master hologram and the at least one holographic blank are in optical contact during exposure to the recording beam and the post-recording beam.
An eighth embodiment of the present invention describes a system for contact recording at least one hologram which includes at least one master hologram, at least one holographic blank, a pre-recording beam, a recording beam, and a post-recording beam, wherein the at least one master hologram and the at least one holographic blank are in optical contact during exposure to the pre-recording beam, the recording beam, and the post-recording beam.